A polymer electrolyte fuel cell (hereinafter simply called “fuel cell”) utilizes the movement of proton through an electrolyte membrane to generate electricity. The electrolyte membrane shows good proton conductivity in the wet state. It is accordingly preferable to keep the inside of the fuel cell in the wet state during operation of the fuel cell, in order to maintain the electrolyte membrane in the adequate wet state.
After the operation stop of the fuel cell, on the other hand, the water remaining inside of the fuel cell or its connection piping is likely to be frozen in a low-temperature environment such as sub-zero environment and deteriorate starting performance of the fuel cell. A proposed technique purges the inside of the fuel cell and the connection piping on operation stop of the fuel cell, so as to reduce the water content remaining inside of the fuel cell or in the connection piping (for example, Patent Literature 1).
The prior art purge method may, however, fail to sufficiently discharge the water remaining inside of the fuel cell (especially remaining in a gas flow path arranged in a power generation area). The purge after the operation stop decreases the system efficiency, so that there is a need to minimize the purges after the operation stop.